Known in the art is the technology providing a speaker, an amplifier, etc. in a charging stand (power supply device) for charging a battery of a mobile phone, converting an audio signal generated in the mobile phone to sound by the speaker of the charging stand, and outputting the sound (Patent Document 1). The charging stand of Patent Document 1 is provided with, in addition to terminals for supplying electric power to the mobile phone, an input terminal receiving as input an audio signal. If the mobile phone is placed on the charging stand for charging, an output terminal provided at the mobile phone and the input terminal of the charging stand will abut against each other. The audio signal generated at the mobile phone is output via the output terminal and the input terminal to the charging stand.
Note that the technology of forming terminals of a charging stand by wire members made of a metal, forming helical portions in the middle of the wire members, and making the terminals of the charging stand and the terminals of the mobile phone abut against each other by a biasing force of the helical portion is known as well (Patent Document 2).    Patent Document 1: Japanese Patent Publication (A) No. 2003-79061    Patent Document 2: Japanese Patent Publication (A) No. 2000-195561